Enlarging the negative. How big?

Depends on how crisp the negative is! If it is razor sharp there is no reason why you cannot enlarge it to its maximum. A thirty-five millimeter negative should be able to produce a 24 x 30 centimeter print with ease and in exceptional cases 50 x 60 cm. To check if the negative is of a good enough quality, enlarge part of the frame to 18 x 24 centimeters, if it looks a bit grainy the chances are that when the whole negative is enlarged to 50 x 60 cm and viewed from a meter away it will look good.

When enlarging to larger sizes you need to take into account the distance that people will see the picture from. Large photos are rarely viewed up close.

Magnification on your enlarger

This is going to get a bit technical, so bear with me! This is the ratio between the print and the negative. It is calculated using the linear rule. To make things easy, lets say we are going to enlarge a thirty-five mm negative (24 x 36 mm) by a factor of ten this will give us a print size of 240 x 360 millimeters ( about 9" x 14") in size.

Magnification is related to the distance the negative is from the enlarging lens and the lens from the baseboard. So as the latter distance increases the former decreases. In other words the higher the enlarging head is from the baseboard the closer the lens gets to the negative when it is being focused and vice versa. It stands to reason that the larger the print the longer the exposure time will need to be. There will also need to be a change in paper grade to a harder one as there is a softening in the contrast.